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There are too many different opinions on proper charging methods for coolers and freezers. I have heard 20 degree superheat at the compressor, clear sight glass, I've even heard someone say you can go as low as 5 degree superheat at the compressor for freezers. I want to be the best Service tech I can be and do it the right way. Can some of you guys tell me the proper way to charge for both TXV and cap tube systems for freezers and coolers. I am very interested in learning correct way.

Originally posted by ace12 ....Can some of you guys tell me the proper way to charge for both TXV and cap tube systems for freezers and coolers. I am very interested in learning correct way.

1. If it's a REAL refrigeration system with a receiver, SG and a TXV.....then charge to a full SG, collect your money and go. If you want to get technical about it, wait until the box is at temperature and shoot for 30 Deg F compressor SH. At the evap outlet, 8 Deg F SH is good, but the compressor SH is the overriding factor.

2. If it's a cap tube system, it's a critically charged system. Weigh in the refrigerant, collect your money and go. As above though, when the system is down to operating temperature the compressor SH (in theory) should be in the 30 Deg F range but you'll find most small factory type cap tube systems are way higher. All you could do then is add a little gas to lower the SH and most often the discharge pressure will go out of sight. Answer.......Don't try to re-engineer a cap tube system with a nameplate charge stated on it. If the facory was wrong, it's not your problem.

I like my Fluke 16 with the beaded probe.
I also carry a raytek infrared meter. LOVE IT!!!

Just this morning, I bought me a pocket sized infra red device. It's the size of a car alarm button pad like you carry on your keychain.

I keep it tucked away safely in my top shirt pocket.

It is so easy to whip it out and take a temperature reading.

I have checked the accuracy against other tools.

($33 .... but dont tell nobody)

I know there's guys here who HATE infra red thermometers. Well ... so what!?
There are also guys here who use dytel and thaw-zone. There are guys here who replace a unit if the start relay fails.

I aint here to get people to be like me, I am here to learn and share knowledge.
If someone shows me a better way of doing somethig ...I will abandone my old methods and follow what thye have shared with me.

It ought to be ditto the other way around too.

Infra red is fantastic, in it's own way.

It is NOT for everything, nor everyone.

But for me, it works great and gives me an edge over having to fiddle around taking a probe measurement.

i use a fluke 52 II digital thermometer with beaded probe. paid way too much for it but its very accurate. So from what i am hearing, 20 degree superheat at the compressor is the most accurate measuement of the correct charge right? This is the same for coolers and freezers whether its cap tube or txv?

What Icemeister said was true. For TX systems, it is easy to adjust what you need for the suction superheat @ the unit. And you will want thirty degrees F, @ the compressor. (At the unit).

I loved my Fluke 52. It was great. Maybe I'll break down and invest in another one someday real soon.

Cap tube systems are a nightmare. Weigh in the called for charge amount, then walk away. Adjust only for oversized driers, if an oversized one was used in place of the size the factory installed as OEM.

Ace,
Most compressor manufacturers recommend a MINIMUM of 20 deg of SH at the compressor. In theory, 1 deg of SH at the compressor would be okay providing there is really no liquid present which would be considered floodback condition. The most effective evaporator is one that has the last drop of liquid evaporate just before it leaves the coil. Since there is margin for measurement error, 5 to 15 deg SH is used.
Our measuring devices can't really tell us more than pipe surface temp. To be safe they recommend min of 20.
On cap tube systems, weigh in charge like said above and same with clearing sight glass on TXV systems.

Best investment, buy a pipe clamp style thermometer to plug into the Fluke 16, 52 etc. Any type K thermocouple thermometer can use one of these. They have SUPER QUICK response time. The Fluke and Fieldpiece models are identical down to the patent number. The Fieldpiece is usually cheaper. Good luck

condenser flood back system charging

Ace,

In a case where you are dealing with a TXV system with condenser flood back controls,ie, units with headmasters or the equivelent, it is best to charge by weight. Charging by clearing the sight glass will only assure you that the system will operate properly between the ambient temperature at the time you charged the system and the maximum ambient design temp of that system. During fall , winter, and early spring when outside ambient temperatures commonly get very cool; these units which had enough refrigerant to operate in the warm summer temperatures will often stop refrigerating completely during colder temperatures. For the flood back system to work properly in colder temperatures, it has to have enough refrigerant to sufficiently flood the condenser with refrigerant in order to maintain head pressure as well as have enough refrigerant in the receiver to maintain a solid column of liquid to the expansion valve. The head pressure created by effectively shortening the condenser is bypassed to the receiver side of the valve in order to maintain adequate pressure on the liquid.
In short with out the "extra" winter charge, the receiver would be robbed (run dry) of necessary refrigerant when refrigerant is back up into the condenser and the unit would stop refrigerating.

hello, friend Put the suction pr.11psig in cap tube) or 31psig in txv system, And them look,and take the superheat and disc-pressure. (this only in a short distance between,comp. and evap. And them tell me what happen.